1. Field of the Invention
The present invention relates to a high-frequency module in which high-frequency components such as chip filters are mounted on a multilayer substrate formed by laminating dielectric layers and electrode layers, and to a communication apparatus including such a high-frequency module.
2. Description of the Related Art
High-frequency modules of the type in which high-frequency components are mounted on a multilayer substrate provided with capacitors and inductors have been used in high-frequency circuit sections of, for example, portable communication terminals in order to reduce the number of parts and to enhance element density in high-frequency circuit sections of, for example, communication apparatuses. For example, high-frequency modules of this type are used in front-end sections of terminals provided in cellular phone systems to reduce the size and weight of the terminals.
The multilayer substrate includes a plurality of dielectric layers and electrode layers, and capacitors, inductors, transmission lines, etc. are formed by patterns of electrodes in the electrode layers. On a lower surface of the multilayer substrate (a surface for mounting on a mounting substrate (motherboard) in an electronic apparatus), a large number of external terminals is provided. Furthermore, on an upper surface of the multilayer substrate, upper-surface electrodes for mounting high-frequency components such as SAW filters are provided, for example, as disclosed in Japanese Unexamined Patent Application Publication No. 2002-118486 (FIG. 4).
Now, the construction of a high-frequency module including a multilayer substrate and a high-frequency component, disclosed in Japanese Unexamined Patent Application Publication No. 2002-118486, will be described with reference to FIGS. 11A and 11B.
FIG. 11A is an external perspective view of the high-frequency module, and FIG. 11B is an exploded perspective view of a main portion of the high-frequency module. A multilayer substrate 1 implemented by a lamination of dielectric layers and electrode layers has upper-surface electrodes and external terminals provided on a surface of the lamination. On a first principal surface of the multilayer substrate 1, high-frequency components 21 and 22 such as SAW filters are mounted.
FIG. 11B is an exploded perspective view showing two layers of the multilayer substrate 1 as extracted. In an uppermost dielectric layer 11, uppersurface electrodes for mounting the high-frequency components 21 and 22, including upper-surface ground electrodes Gq1 and Gq2, are formed. In a dielectric layer 15 near a lowermost layer, a common ground electrode Gd is formed. A large number of dielectric layers is provided between the uppermost dielectric layer 11 and the dielectric layer 15 near the lowermost layer, and the upper-surface ground electrodes Gq1 and Gq2 are directly connected to the common ground electrode Gd by way of via-hole conductors Vdq provided in the dielectric layers. The common ground electrode Gd is arranged to be a ground terminal among the large number of external terminals provided on the lower surface of the multilayer substrate 1.
However, in the high-frequency module according to the related art, for example, if the via-hole conductors are formed without adequately filling via holes with a conductive paste, connection of the high-frequency components 21 and 22 to the ground electrode Gd could become inadequate, possibly causing considerable deviation of electrical characteristics from designed characteristics.
Furthermore, when the number of dielectric layers is larger and the length of the via-hole conductors Vdq becomes longer, the inductance component of the via-hole conductors Vdq increases and grounding of the upper-surface ground electrodes Gq1 and Gq2 is deteriorated, causing inadequate grounding of the high-frequency components 21 and 22.